feat(config): Remove NAT default to stateless NAT mode

[qmonnet]

When the user didn't specify a NAT mode in the CRD, we used to default to static (stateless) NAT. We changed that recently, when we updated to the new user API with commit 018c3a9. Now, when NAT is in use, the mode must be specified explicitly.

As a consequence, we want to remove the fallback to stateless NAT in the dataplane repository. This commit began with simple changes in file config/src/external/overlay/vpcpeering.rs: we remove make_nat() and the Default trait implementation for VpcExposeNat, and update VpcExpose's as_range() and not_as() methods to use self.nat if present. This means that if self.nat is not set, we return an error: because of that, we get to update all the (numerous) calls to as_range and not_as in the tests for crates config, mgmt, flow-filter, and nat.

Having to .unwrap() in the tests after each call to as_range() or not_as() is not particularly pleasant, but seems like a logical consequence from the API change (and internal changes from commit cf20117, where the as_range and not_as lists are now attached to a VpcExposeNat object): if the NAT object has not been configured, it makes no sense to set the NAT target prefixes.

[Fredi-raspall]

The changes look good to me.
Reminder:

• we should be renaming stateless -> static
• stateful -> masquerading

[qmonnet]

Waiting for #1262 to go in first.

[Copilot]

Pull request overview

Removes the implicit fallback to stateless (static) NAT when a NAT mode is not explicitly configured, aligning the dataplane config model and tests with the newer user API behavior.

Changes:

• Removes Default/fallback NAT construction and makes VpcExpose::as_range / VpcExpose::not_as return Result and require NAT to be configured explicitly.
• Updates k8s conversion and multiple crate tests to handle the new Result-returning API (mostly via .unwrap() in tests).
• Adjusts various NAT-related test fixtures to explicitly call make_stateless_nat() / make_stateful_nat() before adding translated prefixes.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
nat/src/stateless/test.rs	Updates stateless NAT tests to unwrap as_range/not_as results.
nat/src/stateless/setup/mod.rs	Ensures exposes explicitly configure stateless NAT before setting as/not_as ranges.
nat/src/stateful/test.rs	Updates stateful NAT tests to unwrap as_range/not_as results.
nat/src/stateful/apalloc/test_alloc.rs	Updates allocator test fixtures to unwrap as_range/not_as results.
mgmt/src/tests/mgmt.rs	Updates mgmt tests to explicitly enable stateless NAT and unwrap as_range.
flow-filter/src/lib.rs	Updates flow-filter tests to unwrap as_range in manifest construction.
config/src/external/overlay/vpcpeering.rs	Removes default/fallback NAT creation; makes as_range/not_as require explicit NAT and return Result.
config/src/external/overlay/tests.rs	Updates overlay config tests to explicitly configure NAT and unwrap results.
config/src/converters/k8s/config/expose.rs	Updates k8s conversion to handle Result from as_range/not_as (currently mapped to InternalError).

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

[qmonnet]

@Fredi-raspall Are we ready to go for this one?